MCA VIGNETTE: Forest Management and a Changing Climate with Diana Six

Diana Six has been studying pine bark beetles for 25 years, and still can’t say she completely understands them. Lately, she’s been diving into a topic she has always found even more confounding - forest management.

According to Six, in the West foresters have gone through two stages of management when it comes to large natural disturbances like pine beetle or wildfire, and now need to pivot to a third in the face of accelerated climate change.

The first stage was called resistance, and was based on the control of nature. “So if we don’t want fires to burn or we don’t want beetles to occur we can stop it, we can resist it,” Six says.

Resistance strategies for fire meant full suppression tactics, such as the Forest Service’s old 10 a.m. rule—all new fire starts had to be out by 10 a.m. the next day. Fire was essentially removed from the landscape, and scientists say that in today’s out of control wildfires we now see the results. For pine beetles, Six says resistance meant cutting every beetle infested tree in a forest and burning it on the spot.

“Then they thin to these very rigid prescriptions, where the forest ends up looking like a spaced cornfield,” she says. The idea is that it will be less likely for beetles to spread through a treated forest because of the distance between trees.

But like fire, trying to push beetles off the landscape eventually leaves forests more vulnerable to them. “The harder you push, the more when it does go it becomes a catastrophic failure. And you know, as long as the conditions exist that will support beetles, those prescriptions will not hold,” Six says.

When managers thin the forest, trees are less vulnerable to beetles in normal years, when the insect numbers are low. But as the hot and dry climactic conditions favorable to beetles occur, conditions eventually reach a point where the beetles thrive. In addition, drought weakened trees are unable to produce the resin healthy trees use to eject the beetles tunneling into their tree trunk. In those conditions, beetles have no trouble infecting what’s been left behind by the well-meaning thinning process. The end result: death of a forest.

Resilience management took hold with the idea that disturbances have an important ecological function for ecosystems, and should be allowed to happen, at least to an extent. Instead, management should prepare the forest for eventual disturbance as much as try to minimize it.

In terms of a management strategy, that means that instead of the well-spaced mature trees of the resistance thinning, where all the young growth is cut out, the forest is left in various stages of age and progression. Younger trees and middle-aged trees are left behind, so that if beetles do pass through and kill the more mature trees, there is a replacement forest already underway in their stead.

Were it not for climate change, Six says, and the changes in the underlying conditions of ecosystems—temperature, moisture and precipitation—that it will bring, resilience management strategies could have been a good idea. Managing forests so they could recover quickly after a disturbance could have mimicked nature’s own regeneration, allowing the forest to return after each incidence of fire or beetle kill.

“But now, with climate change, resilience is still trying to return ecosystems back to a previous state and that’s probably not possible, because the climate’s not going to be the same,” Six explains.

And here is where management runs into a previously unforeseen problem, one that Six believes requires us to find an entirely new perspective. With the rapid rate of change possible for the future, trees will face entirely new conditions—most likely with less seasonal snowpack and longer, hotter and drier summers—that many won’t be able to survive.

It’s possible that some trees could evolve to their new climactic conditions. After all, Six says, “trees have some of the highest genetic variability of anything on the planet.” But for evolution to occur, and to ensure forests can replace themselves after the massive tree die-offs that Six says will result from extended drought, management strategies will have to change.

Within forests, there are likely some individual trees that have a genetic makeup more resistant to drought stress. Six says identifying and supporting those trees might be the only shot to keep western forests near the sizes they are today.

As is, today’s management doesn’t take natural selection into account.

She worries in particular about two of today’s management practices, which run exactly contrary to the idea of letting natural selection function.

The first is salvage logging, which involves cutting out dead wood left behind by beetles or fire, but can also involve taking the living survivors before replanting the entire area of forest. Taking the survivor trees can make the economics work for logging companies, as beetle-infected wood alone has a low value as lumber. But in doing so, the loggers remove the very trees that may have survived the beetles because their defenses were stronger—indicating a higher genetic resistance to the drought that left their neighbors weak.

Another mismanagement technique comes after the logging, according to Six. Or even in cases when there is no logging following a forest disturbances, but when people don't want to wait for the forest to regenerate naturally. That’s replanting, which is mostly done without thought to the genetics of the trees the seeds come from.

By reseeding from trees whose adaptability to drought conditions are unknown, this replanting exhibits the same desire for continuity as full fire suppression or resistance management for beetles. It discounts a changing world, and most poignantly, a rapidly changing climate.

Instead, Six says, we should be identifying the survivor trees. After all, in a weird way big beetle kills can be an opportunity, since the beetles will seek out weaker trees that even scientists can thus far cannot detect.

“It is freaky when mortality kills 90 percent of a stand or beetles kill 90 percent,” Six says, “but we have to realize that when they do it, versus us, there is likely to be natural selection. When we do it, it’s blind.”

A management strategy of the future may be looking at what’s left behind after beetle kill or drought, asking why, and seeing what can be done to promote the survivors' genetics reproducing.

Six is examining the genetics of survivor trees to test her ideas, and is devoting more and more of her time to examining management solutions, a controversial topic.

A recent paper she co-authored on the subject and on much of the ideas described here, titled Management for Mountain Pine Beetle Outbreak Suppression: Does Relevant Science Support Current Policy? received a mixed reaction. While many Forest Service managers issued official rebuttals, Six says many researchers also thanked her for bringing the topic to light and seeking to start more discussion. The paper was published in an open-sourced online journal.

In general, Six worries that forest management will not be able to change course in time to provide a coherent response to climate change. But she says if it is going to, it’s got to happen with adaptation and natural selection in mind.

Still she says, things do change. She remembers giving a talk to a group of forestry professionals fifteen years ago, bringing up the topic of climate change and facing an immediately hostile crowd. Five years ago she went back and gave another talk, something she hadn't thought she’d try again.